The BnGRF2 gene (GRF2-like gene from Brassica napus) enhances seed oil production through regulating cell number and plant photosynthesis

Abstract

Seed yield and oil content are two important agricultural characteristics in oil crop breeding, and a lot of functional gene research is being concentrated on increasing these factors. In this study, by differential gene expression analyses between rapeseed lines (zy036 and 51070) which exhibit different levels of seed oil production, BnGRF2 ( Brassica napus growth-regulating factor 2-like gene) was identified in the high oil-producing line zy036. To elucidate the possible roles of BnGRF2 in seed oil production, the cDNA sequences of the rapeseed GRF2 gene were isolated. The Blastn result showed that rapeseed contained BnGRF2a/2b which were located in the A genome (A1 and A3) and C genome (C1 and C6), respectively, and the dominantly expressed gene BnGRF2a was chosen for transgenic research. Analysis of 35S- BnGRF2a transgenic Arabidopsis showed that overexpressed BnGRF2a resulted in an increase in seed oil production of >50%. Moreover, BnGRF2a also induced a >20% enlargement in extended leaves and >40% improvement in photosynthetic efficiency because of an increase in the chlorophyll content. Furthermore, transcriptome analyses indicated that some genes associated with cell proliferation, photosynthesis, and oil synthesis were up-regulated, which revealed that cell number and plant photosynthesis contributed to the increased seed weight and oil content. Because of less efficient self-fertilization induced by the longer pistil in the 35S- BnGRF2a transgenic line, Napin- BnGRF2a transgenic lines were further used to identify the function of BnGRF2 , and the results showed that seed oil production also could increase >40% compared with the wild-type control. The results suggest that improvement to economically important characteristics in oil crops may be achieved by manipulation of the GRF2 expression level.

Overexpression of Brassica rapa GROWTH-REGULATING FACTOR genes in Arabidopsis thaliana increases organ growth by enhancing cell proliferation

“…These results indicate therefore that the large size of BrGRF-OX organs is due to increases in cell numbers, but not due to increases in cell size. Our data are well in agreement with previous studies in which overexpression of AtGRFs, BnGRF2, and BrGRF8 promoted cell proliferation activities and thus increased organ size (Kim and Lee 2006;Liu et al 2012;Wang et al 2014). In conclusion, the seven BrGRFs examined in this study seem to act as positive regulators of the cell proliferation process, consequently determining the final size of organs.…”

“…In the transgenic plant seeds, the amount of most fatty acids increased compared with the wild-type, however the composition of various fatty acids in the transgenic plant seeds are not significantly changed compared with the wild-type (Supplemental Table 5). Similarly, it has been reported that up-regulation of OsGRF4 in rice and overexpression of BnGRF2 in A. thaliana greatly enhanced the size, weight, and yield of seeds (Che et al 2016;Duan et al 2016;Hu et al 2015;Li et al 2016;Liu et al 2012). In addition, Arabidopsis seeds overexpressing BnGRF2 contained 10% more oil than wild-type seeds (Liu et al 2012).…”

“…Similarly, it has been reported that up-regulation of OsGRF4 in rice and overexpression of BnGRF2 in A. thaliana greatly enhanced the size, weight, and yield of seeds (Che et al 2016;Duan et al 2016;Hu et al 2015;Li et al 2016;Liu et al 2012). In addition, Arabidopsis seeds overexpressing BnGRF2 contained 10% more oil than wild-type seeds (Liu et al 2012). Overexpression of BrGRFs enhances organ growth by promoting cell proliferation…”

“…GRFs also play a role in development of female reproductive organs of A. thaliana (Liang et al 2014), and are expressed in rice embryos and maize ears, suggesting a possible role in regulation of seed growth and development (Ye et al 2004;Zhang et al 2008). A GRF gene of B. napus, BnGRF2, was proposed to be responsible for increases in seed weight, probably by regulating cell number and photosynthesis; these, in turn, might be also responsible for the increased production of seed oil (Liu et al 2012).…”

Relationship of photosynthesis and related traits to seed yield in oilseed Brassicas

“…flowering and siliquae formation are consistent with the findings of other studies in which leaves were reported to be important sources of Pn up to flowering when stems and siliquae become more significant exporters of Pn (Uddin et al, 2012). Increase in Pn was due to increased chlorophyll content (Liu et al, 2012, Sharma et al, 2014. Further, genes associated with cell proliferation, photosynthesis and oil synthesis were unregulated which revealed photosynthesis contributed to increased seed weight and oil content.…”